DRA Benthic Invertebrate Study Update

(As with most issues swirling around the operation of the SWW tower at Round Butte Dam, requirements to protect the river can be confusing at best, or ignored at worst. This article is an attempt to clarify the changes in and permit requirements for the aquatic invertebrates in the lower Deschutes River.)

DRA’s Rick Hafele looks over the area on the lower Deschutes River that will be sampled.

Notable and concerning changes
Anyone who has fished the lower Deschutes River for more than the past 12 to 15 years has observed notable and concerning changes in the timing and abundance of most common insect hatches found in the river.
Hatch surveys conducted by the Deschutes River Alliance have documented this change and found dominant hatches now occur four to six weeks earlier than prior to the operation of the Surface Water Withdrawal Tower (SWW) at Round Butte Dam. In addition, these hatches are less predictable and generally less abundant.

Part of the process is taking underwater photos to document the different sections of the sample area.

Although there are no water quality standards that directly address changes and/or declines in adult aquatic insects, Oregon does have a standard designed to identify impairment to aquatic life due to changes in water quality. Called the Biocriteria standard, it protects aquatic life from pollution and states: Waters of the State must be of sufficient quality to support aquatic species without detrimental changes in the resident biological communities. (OAR 340-041-0011).

The primary aquatic community sampled to determine if this standard is being met is the benthic invertebrate community. Benthic refers to the invertebrates living on the benthos, or substrate, along the stream bottom.

PGE study
As part of Portland General Electric’s (PGE) permit to operate the SWW, the Oregon Department of Environmental Quality (DEQ) required PGE to complete a benthic invertebrate study in the lower Deschutes River before, and after SWW tower construction and operation.

Consultants, hired by PGE, conducted a pre-tower study from 1999-2001 and a post-tower study from 2013-2015. The final report of the studies was completed and released in 2016 (R2. 2016. Lower Deschutes River macroinvertebrate and periphyton study – Final Report. Prepared for Portland General Electric Company. March 4, 2016.).

After collecting the samples, they are organized and prepared for the lab.

That report concluded that there were no significant changes to the invertebrate community after the SWW tower started operating. However, biologists at DEQ identified several issues with how the data were analyzed and notified PGE.

The DRA had similar concerns and hired a professor at Portland State University to take the same data and perform an analysis (See Dr. Patrick Edwards’ Statistical Analysis of R2 Macroinvertebrate Data on the DRA website under Science Reports). This analysis resulted in a different conclusion and found impairment to the invertebrate community post-tower operations compared to pre-tower.

One of the important changes was a significant increase in the abundance of non-insect taxa (primarily worms and snails) compared to sensitive insects like mayflies and stoneflies. This indicates a shift (decline) in water quality necessary to support robust numbers of sensitive aquatic insects.

Since PGE consultants completed their sampling in 2015, there have been no follow-up studies of benthic invertebrates by PGE or state agencies. Because DRA believes invertebrate studies provide critical information on how water quality affects aquatic life in the river, DRA began its own benthic invertebrate sampling program in 2015. The sampling follows DEQ sampling protocols and the samples are processed at a lab in Corvallis specializing in aquatic macroinvertebrate assessments.

Sampling sites
The DRA sampling occurs at two sites (one near Warms Springs and one near Kaskela). These sites were sampled in 2015 and 2016, and again in 2020, 2021, and 2022.

The findings of DRA’s samples from 2015 and 2016 are available in the DRA website Science Report section (2015/2016 Lower Deschutes River Benthic Study). An updated report with the remaining data will be completed in early 2023.

Charts
The charts right, from the 2015-2016 report, show the relative abundance of the non-insect taxa, primarily worms and snails (55-80% of all invertebrates), and EPT species, (mayflies (E), stoneflies (P), and caddisflies (T) (9-34% of all invertebrates). Most EPT species are sensitive to declining water quality, while the non-insect taxa are tolerant of poorer water quality.

The high percentages of non-insect taxa indicate that water quality changes from SWW operations are negatively impacting aquatic life in the lower Deschutes River and suggest likely violations of the state’s Biocriteria standard that should be investigated by DEQ.

Deschutes River Alliance: Cooler, cleaner H2O for the lower Deschutes River. 

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